Method of purifying carbazole ester precursors of 6-chloro- alpha -methyl-carbazole-2-acetic acid

摘要

A process of purifying a (6-chloro-2-carbazolyl)methyl-malonic acid di(C1-C6 alkyl) ester of Formula (I): wherein Ra and Rb must be the same and are selected from the group consisting of C1-C6 alkyl; comprises phase separating one or more impurities from said carbazole ester at least once wherein the solvent used to carry out said phase separation is acetic acid. In a preferred embodiment said acetic acid is glacial acetic acid which is maintained at a temperature of from about 30 DEG to about 110 DEG 0 C. and said carbazole ester is obtained in a purity of at least 99.90% by weight, so that the amount of impurities present therein is 0.10% or less by weight. In a more preferred embodiment of said process, said temperature is from about 50 DEG to about 70 DEG C., and said phase separation is carried out only once.